1. Field of the Invention
The present invention relates to an image recording method which is used for a reversible thermosensitive recording material capable of reversibly writing an image thereon and erasing the image therefrom by the application of heat thereto, more particularly to an image recording method applicable to a rewritable card with a thermosensitive display applied thereon used as a prepaid card or a credit card.
2. Discussion of Background
In recent years, there has been a demand for a thermosensitive recording material which is rewritable without using paper for saving natural resources. For instance, a rewritable thermosensitive recording material, which comprises a support and a thermosensitive layer formed thereon comprising a resin such as polyvinyl chloride resin or polyester resin, and an organic low-molecular-weight material such as higher alcohol or higher fatty acid dispersed therein is known as the most promising recording material as disclosed in Japanese Laid-Open Patent Applications 54-119377 and 55-154198.
Recording, that is, image formation and erasure by use of this type of reversible thermosensitive recording material is performed by utilizing the changes in transparency of the thermosensitive layer therein depending upon the temperature thereof. Therefore, both of the image formation and erasure can be carried out by use of a device such as a thermal head or a hot stamp employed for conventional irreversible thermosensitive recording materials.
Recently, attention has been paid particularly to a reversible thermosensitive recording material employed as a display medium for use with a card such as a prepaid card or a credit card. As a heat application member for such a card, a heat-application roller or a thermal head is usable, however it is preferable to use a hot stamp by which heat can be speedily and uniformly applied to a recording material at a portion thereof.
A conventional hot stamp generally has such a structure as shown in FIG. 1(g). In FIG. 1(g), the contact surface of a hot stamp 11 with a display medium 5 is made of a metal or a metal on which a lubricating material is coated. Reference numeral 2 indicates an infrared lamp, and reference numeral 3, a temperature sensor in FIG. 1(g). Image formation and erasure are performed on the display medium 5 by the application of heat thereto by the hot stamp 11 on a supporting base 61. The hot stamp 11 is movable in the directions of the arrows.
When image erasing is performed by use of a hot stamp on a display medium, it is possible to occur that the card and the hot stamp are not brought into uniform contact with each other even by a slight unevenness of the surface of the card or by the adhesion of foreign materials to the card, heat is not uniformly conducted to the reversible thermosensitive recording material on the card, and images thereon are erased only in lines or in spots.
In particular, when image formation and erasing are performed on a thick card made of polyvinyl chloride such as a credit card, there is a phenomenon that the card is deformed during repeated use thereof, so that it becomes difficult to bring the hot stamp into uniform contact with the deformed card.
In contrast, when the pressure to be applied to the hot stamp is increased, the hot stamp can be easily brought into uniform contact with a reversible thermosensitive recording material. However, when the pressure applied to the hot stamp is increased too much, the card may be deformed or the deterioration of the reversible thermosensitive recording material may be promoted.
Furthermore, in the case where image erasure is performed by use of a hot stamp on a card with minute concave and convex portions such as emboss, which originally exist on the card, the card and the hot stamp are not easily brought into uniform contact when the pressure to the heat stamp is increased.